Micro-vapor pressure apparatus



Feb. 24, 1959 'A. Y. MOTTLAU 2,874,567

r MICRO-VAPOR PRESSURE APPARATUS Filed Dec. 5, 1955 2 Sheets-She et 1 41 zi f I 3 uui' I) ll'lllll lk )Illllllllllll||lll|lll llIlljllllllllllllllllllllI!II !IIL| lillllllll? llllllllllllllllllllllllllllllllllllllllllllllllllllllllllll Fig. I

August Mottlou Inventor By Attorney Feb. 24, 1959 'A. Y. MOTTLAU 2,8745

MICRO-VAPOR PRESSURE APPARATUS Filed Dec. 5, 1955 2 Sheets-Sheet? Fig. 4

August Y. MOHICILI Inventor WWW I Attorney United States Patent MICRO-VAPOR PRESSURE APBA'RATUS Y. Mottlau, "Clark, 'N. J., assignor to Esso Research and -Eng neering Company, a corporation of Delaware Application December 5, 1955,:SeriaLNo. 550,922

1 Claim. (Cl. 7 3.53)

The;present invention relates to an apparatus for measuring the vapor :pressure of liquids. Particularly, the invention relates to r the determination of the vapor pressure-of volatile, non+viscous liquids, specifically including petroleum products. The invention further relates to means for making such vapor pressure determination whereln samples of extremely small volumes are employed. -Accordingto the present invention, sample volumes of about 1 milliliter may be employed, as'compared with sample volumes of as much as 130 milliliters, or more, when conventional systems are employed.

1A .staindardm'ethod of test for vaporpressure of volatile liquids of the nature now contemplated isthat known as theiReid"Method,fas'set forth by the American Society for Testing Materials, Philadelphia, Pennsylvania, and designatedas-A. S. T. M. D. 3323-52. Although this method is currently'accepted as standard, apparatus now contemplated is less curnbersome, less subject to errors, and employs a sample handling means whichmarkedly reducesvolatility, loss and'va riation. The apparatus of the present invention further provides a reproducible standard deviationof :0.022 p. s. i., as compared with the standard deviation in'the'order of 0.5 ps. i. attainable by conventional methods.

It is an object of the present invention to provide an apparatus for making of vapor pressure determinations which ishighlyaccurate, but simply and rapidly-accom plished. It isalso an object of the inventionto provide an apparatus which may be employed to produce results whichare readily correlated'with the results produced by the Reid'Method, and which may be'ernploye'd accurately to predict Reid Vapor Pressure values. It" is a further object of the invention to provide an apparatus suitable foremployrnent in making Micro Vapor pressure determinations, including an evacuable sample receiving chamher, and means 'for'maintaining the volume and temperature of such chamber substantially constant.

The invention "and its objects "maybe more clearly understood from the following description, when it is read in conjunction with the accompanying drawings in which j 'Fig. l'is a schematic illustration of the apparatus in side elevation and partly in verticalsection.

Fig.2 is an enlarged view in'sidee'levation and partly in'vertical section of an accessory part of theap'paratus of Fig.1 in its functionalrelation to-the structure'thereof.

Figs. 3 and '4 are similar views inwertical section of other accessory parts of the apparatus of'Fig. 1 in their functional relation thereto.

Referring now to the drawings, in Fig. l, the numeral 1 designates anevacua'ble chamber which, as shownincludes Ia dependent conduit leg :portion 2 and side :arm portionS. The .leg'portion 2 .is provided with atwo way valve 4 adapted for alternate eomrnunigation between the deg-2 and tone of'two conduits S and 6. The ,conduit 5 provides 2 1 5 t d a in th hambe :4- he i nu t fi i renamed t a suutntpum 7 through a rap 8 later referred to.

2,874,567 =Ra-tented :Feb. 251,1959.

. 2 The side arm portion 3, as shown, isformed integrally witn'one-leg 9 of a U-tube mercury manometer, cornmun cating directly therewith. In generaL'the side arm portion '3 and the upper end of the leg 9 may beco'n-v sidered as meeting in a horizontal plane common to an indicia snark designated by the numeral 10, the arm .3 extending .upwardly therefrom to form an inverted U-bend connection with the chamber 1 intermediate the upper and lower ends thereof. The operating capacity of the chamber 1 isdefined between the mark 10 and a similar mark at an intermediate level of the conduit 2 which is designated by the numeral 19. The upper end of the leg 9extends downwardly from the terminal end of the arm 3 to torm 'an enlargement or bulb 11, having a capacity or volume substantially equal to the volumeof thechamher 1. Downwardly beyond the bulb 11, the leg 9 ,is provided with two valves 12 and.13 respectively disposed in vertically spaced relation, one to another, forpurposes later described. Beyond the valve 13, the leg 9 commignicates directly with the other and second leg14 of the U-tube -manometer through a U-bend portion 15. At its upper-end, the second manometer leg opens directly intothe surrounding atmosphere.

At its lowermost level, the U-bend portion 15 is provided with a dependent nipple 16 which provides-a coupling means for a flexible conduit 17, attached at one end "to the nipple. -At the other end, the'conduit 17 is attached to an'open reservoir bulb or container 18. The manometer as well as the container 18 and conduit 17are adapted to receive and contain a volume of mercury adequate for the purposes later indicated and described. In efiect,'the container 18 and conduit 17 provide a third manometer leg of variable height, whereby the height of the'columns of mercury in the other two legs maybe varied as required according to the present invention. In the apparatus illustrated by Fig. 1, an elongated strip of mirror glass is provided as a backingfor theleg 1'4; This strip of glass is designated in the drawing by the numeral 20. As shown, it is provided with avertical series of horizontal indicia markings adapted to indicate the h'eight-of acolumn of mercury in the leg 14 in centimeters.

Asshown in Fig. 1, the upper end of the chamber "1 is closed by means of a partition 21, the walls of the chamber 1 extending upwardly beyond the partition to form a receptacle or container 22. The partition 21 is provided with an orifice '23 opening between the "container '22 and the chamber 1. Inasmuch as the system contemplated according to the present invention is a mercury system, the orifice 23 is a mercury orifice, namely, one which is gauged to inhibit the'passag'e of mercury therethrough by gravity under anypredetermined headiof a body of mercury which may be "contained in the receptacle 22 therefor. The orifice 23, by reason of its size and character also tends somewhat to restrict or inhibit flow when a pressure differential 'may be imposed across the orifice by evacuation of the chamber, or by the vapor pressure of a material introduced into the chamber. A positive seal'is provided, however, by

means 'of a plug element2 4 adapted to fit "the -orifice.-

As shown more clearly in Fig. 2, the-orifice 2312 is membe'rvprovided with 'a tip portion adapted to match andbe seated in theorifice 23. The ap ortion-mayb un r l or sn ru r swa as shb n m y be provided with an added conically 'shaped sleeve '26 of a material such "as plastic to provide the desired setil with t Weighted, "as'by a superposed housing filled with are:

orifice wall. Preferably, *the plug *eleme'nt'fi's The housing, as shown, is 28, including a handle 29.

The accessory part as illustrated able to that illustrated in Fig. 2, except that for the plug element 24, there is substituted a'tubular element 31. The tubular element 31 is similarly provided with ,afshaped tip portion32 and a seal sleeve 33, however, as .well as with a housing 34 containing shot 35 as weighting means. The element 31 extends through the housing 34 andra closure. 36 therefor'to provide a handle portion37. The part as shown by Fig. 3 is more specificallyzdesignated as a vacuum breaker, and its function is laterdescribed. With further reference to Fig. 1, the chamber 1, and including at least a portion: of the associated mercury receptacle 22 and the side arm portion 3,'as well asat. least a portion of the upper ends of'dependent-conduitiz and manometer leg 9 are enclosed in a'fiuid reservoir housing 41; The housing 41 is provided for; circulation of a heat exchangefluid therethroug'h as by means of inlet and outlet conduit connections 42 and'43 respectively. I The housing is also provided with'a necked orifice 44 adapted to receive-a thermometer 45 passedjtherethrough and held in fluid tight relation by means of a stopper '46;

The accessory part as shown by Fig. 4, is a means for introducing a liquid sample into the chamber 1 after evacuation thereof. As. shown, this means comprises a closed mercury bulb 51, having side arm conduit'portiou 52 opening therefrom at the upper end. An inverted U-shaped pipette having opposite vertical legr portions 53 and 54 of unequal length is associated with the bulb, with the shorter legportion 53 extended through the upperend of the bulb, in fiuid tight relation thereto,- and down- Wardly therein into closely spaced relation to the lower end of the bulb. The lower end of each leg portion is provided with a special tip portion. The tip55 of the leg portion 53 has a capillary bore of such small diameter that mercury contained in thebulb 51, and indicated there by the numeral56, cannot enter the bore unless a pressure equivalent to from about millimeters to about millimeters of mercury above atmospheric pressure is applied to the bulb through the side arm 52. The tip 57 of the leg portion 54 is drawn and ground to fit the orifice'23 in the partition 21, and to provide a substantiallyvsealedjoint therewithrwhen the tip is inserted in the orifice. The tip orifice is preferably gauged to a diameter of "about 0.15 millimeter. *The pipette legs 53and 54, as well as the cross-over connection between them, have a capillary bore 58 slightlylarger than that ofthe tip portion 55. In addition, in the leg portion 53, the bore is enlarged as at 59 to form additional capacity for the pipette. This capacity is proportionally related to the volume of the chamber 1 of 'Fig. 1. ratus contemplated, the pipette 'capacityis gauged to a volume about one-fifth that of the chamber 1 as defined between the junction of side arm -3 with the. upper 'end of the manometer leg 9and a predetermined intermediate level in'the dependent conduit 2. In Fig. 1, this intermediate level'is designated by the numeral 19.,

' In employing the apparatus as illustratedand described,

a level of mercury is first established in the receiver 22 such as to provide a head which in cooperation with the plug element, will balance a pressure in the chamber 1 closed by means of stopper by Fig. 3 is compar- 10 is approximately equal'to one atmosphere. a

With plug 24 in the orifice 23, valve 4 is turned to connect the conduit 2 with vacuum pump 7 through the trap 8. With the pump connected, the pressure in the system including chamber 1, conduit 2, side arm 3, and leg 9 above the valve 13 is reduced to or below that of approximately 0.5 millimeter of mercury. At this point, the valve 13 is opened slowly .to permit mercury to enter from the reservoir 18 and as may be required to exactly position the upper level of mercury in the leg 9, at the mark 10. To do this, pumpingis continued while the reservoir 18 is raised or lowered to introduce or withdraw mercury to or from the manometer. leg 9. Valve 4 is then closed and the plug 24 is raised in order to introduce mercury from the container 22, to a level in the leg 2 at the mark 19. At this point, the level of mercury in.

the leg 9 is checked and reestablished at the mark 10 if necessary. The level of mercury in the leg 14 is then recorded. The valve 12 is then closed and the apparatus is ready for introduction of the sample liquid into the chamber 1.

Theliquid' sample to be tested is prepared according to the procedure specified for the Reid method, under the above referred to specification ASTM D. 323-52, and the temperature of the water circulating through the housing 41 previously has been brought to a substantially constant temperature of 100 F. With the sample prepared as specified, the pipette of the accessory part shown in Fig. 4 is filled with mercury by exerting the. re-l quired pressure through the side arm 52 upon the mer-' cury contained in the mercury bulb 51; Due to' the greater length of the arm 54 over the arm 53, when the bore of the pipette is filledwith mercury there will be no reverse flow thereof as long as the tip 57 is retained at a level lower than that of the tip 55. In such a position, the tip 57 is dipped into the sample and with the tip 57.

Y covered by the sample, the pipette is then slightly tilted 5 milliliters plus or minus 0.03 milliliter, the capacity In the .appasubstantially equal to the estimated vapor pressure of a liquid to be tested. I j

With valves 12 and 13 open, and valve 4 turned to is introduced into or withdrawn from the manometer by means of the reservoir 18 and conduit 17 tofprovide' an of the pipette bore should be about 1.0 milliliter plus or minus 0.003 milliliter, or /s the internal volume of the chamber 1. With the sample contained in the pipette, the leg 54 is introduced into the'mercury con: tained in the receptacle 22 and withdrawing the plug element 2 4,,the tip-57 of the'leg 54 is quickly inserted into the orifice 23. 'At the pressure existing in the cham-' her 1, the sample contained in the pipette is then drawn I from the orifice 23 and replaced by the plug element 24.-

It is to be expected that during this operation, -a small amount of mercury may be drawn into the chamber from the receptacle 22 and also from the bulb, 51 through the pipette 54. This mercury will pass downwardlyinto l the conduit 2 and after ,introduction'of the samplemay;

be withdrawn therefrom to re-establishthe mercury level.

in the'conduit. 2 by briefly reconnecting the conduit ,2 to the vgcuum pump 7 through the valvel4, conduit 6 and trap F f 1 The valve 12 is'now opened. slightly whileraising the mercury reservoir 18 and thereby introducing mercury into the leg 14, raising the level therein to balance the pressure ofthe-chamber 1 as produced by the' vapor pressure of the sample liquid therein 'a'n'd to maintain the level of themerc'ury in the legs, coificid'entwith the mark 10. When steadinessof the lvel of the leg 9 indicates that an equilibrium pressure has becn reached, the level of mercury in the leg 14 is again recorded. The difference between the initially recorded level of mercury in the leg and that recorded after equilibrium pressure has been achieved is indicative of the vapor pressure of the sample liquid and may be directly read as the pressure of the column of mercury above the initially recorded level in the leg 14.

'lhe apparatus may be employed, according to the method described, for testing successive samples when P P d in the manner now described. The valve 12 i fi closed in order to maintain the predetermined volume of the chamber 1, and substantially to avoid entrance 0f apors from the first sample into the leg 9. The P g is then replaced with the vacuum breaker 31, shown in Fig. 3, and the valve 4 turned to establish communication between the leg portion 2 and the conduit 5. when y r maining liquid portion of the previously tested sample has been drained fron the chamber 1, through the conduit 5, suction may be applied to the conduit 5. In this manner any remnants of the previously tested sample may be evaporated from the Walls Of the chamber. The vacuum breaker 31 may then be replaced by the plug 24, and the apparaus is then ready for another testing operation substantially as already described.

Inasmuch as the testing prtccdure is initiated with a. pressure in the chamber 1 subsantially below atmospheric pressure, in order to transla t result btained to terms of Reid Vapor Pressrre, allowance m b6 made; for the partial pressure of air dissolved in the test sample. In other words, the ditfercnce, in millimeters of mercury, between the initially recorded level of mercury in the leg 14 and the final level therein, represents the vapor pressure of the sample itself plus the partial pressure of the air dissolved inthe'sample introduced. This air may be presumed to have come out of solution at the reduced pressure, of the test chamber.

As a first step in such translation of values, the nu- .merical value of the mercury level difference in millimeters is multiplied by 0.01934 to convert the total vapor pressure of the sample evidenced and expressed in millimeters of mercury to a pressure value expressed in pounds per square inch. This pressure in pounds per square inch is designated as MVP (micro vapor pressure). This value is substituted in the following equation to obtain a predicted Reid Vapor Pressure (PRVP): PRVP=0.9096 (MVP) 0.35.

Although the apparatus has been described with par ticular reference to vapor pressure determinations wherein the chamber 1 is to be maintained at a temperature of F., the operation may be conducted at higher or lower temperatures where the materials tested may have either extremely low or extremely high vapor pressures. Also, prior to introduction into the testing apparatus these materials may be initially heated or refrigerated as required to facilitate accomplishment of the determination.

What is claimed is:

An apparatus for determing the vapor pressure of vaporizable liquids, comprising a sample receiving chamher, a first conduit connection communicating with and dependent from the bottom of said chamber, means for introducing mercury through said chamber into said dependent conduit connection including a mercury orifice opening into said chamber and a closure for said chambet, a second conduit connection communicating with said chamber in vertically spaced relation to said first conduit connection, a U-tube manometer in direct communication with said second conduit connection through the upper end of a first leg portion of said U-tube, the second leg portion of said U-tube extending upwardly beyond the connection between said second conduit and said first leg, heat exchange means including a housing and means for circulating a heat exchange fluid therethrough disposed to enclose said chamber said second conduit connection and at least that portion of said first conduit connection immediately adjacent said chamber, means for introducing and withdrawing mercury into said U-tubc, said means adapted to establish and maintain opposed columns of mercury in said U-tube wherein the upper end of the column of mercury in said U-tubc first leg substantially limits the volume of said chamber, means for evacuating said chamber, means for introducing a sample portion of said liquid into said chamber through said mercury orifice, and means for indicating the upper surface level of mercury in the second leg portion of said U-tubc manometer.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,731 Fairbairn Dec. 8, 1942 2,323,556 Mattocks July 6, 1943 2,418,379 Wallace Apr. 1, 1947 2,540,377 Pachaly Feb. 6, 1951 

